The site did not officially reveal why it was necessary to close the entire forum without warning except that ''a number of posts'' did not conform to the site's ''standards''.

A message on the Thorn Tree page said the forum was closed ''temporarily'' so the site could apply ''necessary editorial and technical updates''.

The founder of Lonely Planet, Tony Wheeler, who no longer owns the publisher but contributes to it, said he was amazed the forum was still offline four days after the shutdown and criticised the BBC for not offering a more detailed explanation.

Thorn Tree is about 16 years old and has become a staple for avid travellers looking for tips, advice and a connection with other globetrotters.

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A source with links to Lonely Planet management said the decision to shut the forum was ''all about Jimmy Savile''.

The source said a user, who had been banned several times for trolling and harassment, emailed BBC executives asking if they were aware Thorn Tree was full of porn and swearing.

''They discovered that if you looked for terms like 'paedophile' or 'child prostitution', you got Thorn Tree hits,'' the source said.

''The hits are mostly discussions of current events or pointless stuff that would have been moderated, like 'Barney the dinosaur is a big purple paedophile'. However, someone found a thread about 'what's the age of consent in Mexico?' That really set them off.

''They went into full, freak-out, panic attack mode.''

The source said other posts the executives found objectionable were related to child prostitution in Thailand.

Long-time Thorn Tree users are distressed they got no warning of the shutdown and did not have a chance to say goodbye. It is not clear when the site will be back online. In the past, some have labelled Thorn Tree ''scorntree'' after experiences with abusive trolls on the site.

BBC Worldwide spokesman Philip Fleming said BBC had found no evidence of discussions concerning paedophilia on Thorn Tree "but we have discovered instances of inappropriate language and themes"."Until we are confident that all these rogue posts can be identified and deleted, we feel we have no option but to temporarily close the site as a precautionary measure," Fleming said.

Lonely Planet was started in Melbourne by Maureen and Tony Wheeler in 1972. The pair sold a 75 per cent stake to BBC Worldwide in 2007 and the final 25 per cent in February 2011.